1. Field of the Invention
The present invention relates to an adhesive label and an apparatus for producing the same.
2. Description of the Related Art
As conventional and general adhesive labels, there are widely known adhesive labels which have a printing surface on one side and an adhesive surface on the other side and which are wound into a roll shape or formed into a sheet shape.
Those adhesive labels are usually kept or stored while being overlapped with one another. Therefore, there is known an adhesive label which has the adhesive surface covered with release paper so as to prevent the adhesive labels from adhering to one another. Such an adhesive label is peeled from the release paper for use, and the release paper is disposed of as waste after being used. When an adhesive label is produced by a printing apparatus such as a printer, peeling the adhesive label from the release paper after production has been cumbersome.
As described above, the conventional adhesive labels have various problems regarding the protection of environment, labor, and cost.
In recent years, in view of those problems, there have been proposed adhesive labels in which an adhesive surface of an adhesive label is formed of a thermosensitive adhesive agent, which makes it unnecessary to use the release paper. That is, the thermosensitive adhesive agent used on the adhesive surface is usually non-adhesive, but exhibits adhesiveness by being heated to a predetermined temperature or higher. Therefore, such an adhesive label has no adhesiveness when being kept or stored, and hence the release paper is not required.
The configurations of such an adhesive label and an adhesive sheet using a thermosensitive adhesive agent are described in Japanese Patent Application Laid-open Nos. 2000-103969 and 2006-083196.
Specifically, Japanese Patent Application Laid-open No. 2000-103969 describes the configuration of an adhesive sheet having high adhesiveness after being heated and an excellent anti-blocking property which does not allow blocking to occur even when the adhesive sheet is kept for a long period of time in an unheated state, by using a thermosensitive adhesive agent on an adhesive surface.
Further, Japanese Patent Application Laid-open No. 2006-083196 describes a thermosensitive adhesive label that can be activated with low heat energy and that is excellent in an anti-blocking property and adhesive strength with respect to a rough adherend as well as a smooth adherend.
Specifically, both Japanese Patent Application Laid-open Nos. 2000-103969 and 2006-083196 use a thermosensitive adhesive agent containing a synthetic resin, a solid plasticizer, and a tackifier on an adhesive surface. During heating, the solid plasticizer is melted to allow the synthetic resin to swell or to be softened, and the tackifier causes the adhesive surface to exhibit required adhesiveness with respect to the adherend. That is, in the adhesive label and the adhesive sheet using the thermosensitve adhesive agent of Japanese Patent Application Laid-open Nos. 2000-103969 and 2006-083196, the adhesive surface is kept in a non-adhesive state at room temperature and exhibits adhesiveness by being heated to a predetermined temperature or higher. Therefore, the blocking can be prevented while such an adhesive label and an adhesive sheet are kept or stored at room temperature, which renders release paper unnecessary. Thus, an attempt is made so as to obtain the effects of protection of environment and the reduction in cost involved in the reduction of the number of parts.
Meanwhile, the following patent documents describe other configurations of an adhesive label.
Japanese Patent Application Laid-open No. Hei 09-111203 describes the configuration in which a layer made of a pressure-sensitive adhesive agent is provided on one surface of a base sheet, and the surface of the layer is covered with a microcapsule, to thereby prevent blocking caused by adhesion of the sheets even when the sheets are kept or stored while being overlapped with one another. Specifically, a thermally readily breakable microcapsule layer is provided on the surface of the pressure-sensitive adhesive agent layer, which prevents the adhesive strength of the pressure-sensitive adhesive agent layer from being exhibited during keeping and storage. When the adhesive strength is required, the microcapsule is broken thermally and the lower pressure-sensitive adhesive agent is exposed. Thus, the adhesiveness is exhibited.
Japanese Patent Application Laid-open No. 2006-78733 describes the configuration of an adhesive label in which a recording surface is formed on one surface of a base and an adhesive surface made of a pressure-sensitive adhesive agent is formed on the other surface, and the adhesive surface is covered with a non-adhesive resin film. In this manner, the blocking is prevented during keeping and storage. When the adhesive strength is required, a resin film is opened by being heated selectively, and the lower adhesive agent layer is exposed through openings, to thereby adhere the adhesive label to an adherend.
That is, the adhesive labels in which an adhesive surface is covered with a microcapsule or a resin film described in Japanese Patent Application Laid-open Nos. Hei 09-111203 and 2006-78733 are the same as those of Japanese Patent Application Laid-open Nos. 2000-103969 and 2006-083196 in that release paper is not required. However, in Japanese Patent Application Laid-open Nos. Hei 09-111203 and 2006-78733, an attempt is made so as to obtain stronger adhesive strength by using a pressure-sensitive adhesive agent on an adhesive surface. Then, by covering the surface of an adhesive surface with a non-adhesive microcapsule or resin film layer, the anti-blocking property at a time when the label is kept while being wound into a roll shape or overlapped is enhanced. On the other hand, when adhesiveness is required, openings are formed by thermal breakage of the microcapsule and the thermal contraction of the resin film, and the adhesive surface is exposed through the openings to obtain adhesive strength.
The solid plasticizer contained in the thermosensitive adhesive agent used in the adhesive label as disclosed by Japanese Patent Application Laid-open Nos. 2000-103969 and 2006-083196 has a glass transition point (Tg) of room temperature or lower, and most of the solid plasticizers are usually activated at room temperature or lower. Therefore, even in a kept state at room temperature, some adhesive strength is exhibited inevitably.
That is, it is difficult to bring a thermosensitive adhesive agent layer fully in a non-adhesive state when the layer is stored at room temperature. Therefore, there is a possibility that adhesive labels overlapped with one another adhere to one another to cause a blocking phenomenon. Further, there is a problem that it is difficult to obtain strong adhesiveness properties due to composition properties of a thermosensitive adhesive agent.
In order to solve those problems, it is conceivable to set the glass transition point of the solid plasticizer, at which the solid plasticizer is activated, to be higher than room temperature to suppress the adhesiveness at room temperature, and thus prevent blocking. However, simultaneously, large heat energy is required for exhibiting sufficient adhesiveness.
On the other hand, in order to obtain strong adhesive strength with the above-mentioned configuration, that is, adhesive strength adapted to various adherends, it is conceivable to form a thick layer of the thermosensitive adhesive agent. However, in this case, there arise problems that larger heat energy is required, and a power source capacity of a heat source needs to be increased, etc.
In short, it is difficult to prevent a blocking phenomenon at room temperature and ensure high adhesiveness with relatively low heat energy at the same time.
Further, the solid plasticizer contained in the thermosensitive adhesive agent has crystallinity depending upon temperature. Therefore, the solid plasticizer causes a rapid decrease in adhesiveness caused by recrystallization after thermal activation. It is necessary to use a special solid plasticizer depending upon the storage environment and use environment so as to ensure certain adhesive strength. Thus, there is a problem regarding mass-productivity.
Further, when a thermosensitive adhesive agent is melted by heating, using a thermal head of a thermal printer or the like as a heat source, the thermosensitive adhesive agent is directly brought into contact with the thermal head. Therefore, the molten adhesive agent adheres to a thermal head, a platen roller opposed to the thermal head, a paper feed path, etc. as paste dirt, which may lead to the failure of transportation of an adhesive label and the occurrence of a paper jam.
In order to solve the problems of the thermosensitive adhesive label, in particular, the problems regarding blocking and heating efficiency, the configurations of adhesive labels using a pressure-sensitive adhesive agent as described in Japanese Patent Application Laid-open Nos. Hei 09-111203 and 2006-78733 have been proposed. However, for example, when the microcapsule proposed in Japanese Patent Application Laid-open No. Hei 09-111203 is used, it is difficult to exhibit adhesiveness effectively. That is, the following problems are noted. The microcapsule has a spherical shape, and hence, is heated in a point contact with a heat source such as a thermal head or the like. Therefore, the heat conductivity is poor, and effective breakage cannot be performed. In addition, a shell of the capsule remains on an adhesive agent to weaken adhesive strength, or the shell adheres to the thermal head as a heat source to further degrade heat, efficiency. Thus, required adhesive strength cannot be obtained sufficiently.
On the other hand, as proposed by Japanese Patent Application Laid-open No. 2006-78733, when the surface of the pressure-sensitive adhesive agent layer is covered with a resin film layer, the adhesive strength which is originally intended to act on an adherend causes the resin film to be adhered or fixed, which leads to become a factor for inhibiting the thermal deformation and thermal contraction of the resin film by heating. Further, the following problems are noted. The heat efficiency is poor depending upon the material of the resin film, and thus, a thermal head having high temperature properties is required so as to form openings. When a thermal printer that is driven with small electric power is used, heat energy cannot be controlled efficiently. Therefore, the resin film cannot be opened sufficiently, and consequently, required adhesive strength cannot be obtained.
The conventional adhesive labels described above do not require release paper. However, in order to allow the adhesive labels to be non-adhesive at room temperature and to exhibit adhesiveness properties by heating, there is a common technical problem that heat energy increases.
Considering the reaction of the material by heating, first, increasing the temperature of the material to be heated to induce the reaction is a basic precondition. Further, it is known that, from the viewpoint of heat capacity, the increase in temperature of the material is mainly caused by a specific heat and mass of the material to be heated, and a small specific heat of the material and a small layer thickness with a small amount of coating are advantageous. However, the adhesive label is generally targeted to an unspecified adherend. Therefore, the coating amount of an adhesive agent of the adhesive label tends to increase.